The present invention relates to a wireless communication network having a reconfigurable infrastructure, and particularly to such a network in which communication channels are provided to distributed base stations via optical fiber cables.
In wireless communication systems traffic densities in a particular area are not constant. Wireless networks are usually laid out as a set of cells, which provide coverage of a larger region. At certain times, traffic increases in certain cells, providing so-called xe2x80x98hot-spotsxe2x80x99. If hot-spots occur in the network, traffic demand may exceed the network capacity available (in the microwave carrier available in that cell, and/or in the network feeding the wireless base station which supports the microwave antenna in that cell), leading to rejection of calls.
Current wireless systems are divided into cells. Each cell uses one or more dedicated carrier frequencies, with each carrier frequency carrying a limited number of voice or data connections. The carrier frequencies available in a wireless network are usually assigned amongst the cells in such a way that adjacent cells use different frequencies, in order to avoid interference problems. A common network structure consists of hexagonal cells with the transmit/receive antenna at the base station in the middle, arranged in a cluster containing seven cells. Each of the seven cells operate at different carrier frequencies. By repeating this cell structure a large geographical area can be covered. However, this fixed configuration is not responsive to changing traffic densities.
Reconfigurable wireless networks have been proposed to provide communication systems which are responsive to traffic densities. Where traffic density is expected to be dense, cells can be partitioned into smaller micro-cells, each having their own antenna and the flexibility to assign one or more carrier frequencies per micro-cell as needed.
The benefits of partitioning each of the xe2x80x98macro-cellsxe2x80x99 cells into seven (hexagonal) micro-cells surface when extra capacity is needed suddenly at certain locations in the network. At hot-spots (i.e. micro-cells where traffic density is high) one or more additional carrier frequencies may be applied. The whole network may be partitioned into micro-cells when the traffic is intense all over the region. In the case of a hot-spot in the network, the micro-cells may be arranged such that the full capacity of one or more carrier frequencies is offered to the hot-spot micro-cell, leaving the surrounding cells at a less intense coverage as appropriate. In the opposite situation, it is appropriate to restructure the cells such that capacity is shifted from a xe2x80x98cold-spotxe2x80x99 (i.e. where traffic density is low) to surrounding cells. Thus several cold-spot micro-cells may share the same carrier frequency.
The partitioning of the original networks cells into micro-cells may also be implemented by segmenting the cells or micro-cells into a multitude of parts or segments by using a multi-sector antenna (instead of an omni-directionally radiating one). The advantage of this is that no new antenna pole locations need to be acquired; the omni-directionally antenna on the pole has to be replaced by a multi-sector one. Similarly, as described before the cells in a network may be segmented as needed. Also, in a particular segment, multiple carrier frequencies may be stacked. Multi-sector antennas to apply segmentation need to be activated only on those locations where hot-spots are to be expected.
The implementation of the feeder network for the above-described reconfigurable wireless network can be done by a passively split optical network (PON). In a PON, the optical signals in the feeder fiber coming from the head-end section are split among many drop fibers entering the so-called optical network units (ONUs) close to (or at) the base stations. By means of optical fibers, this splitting ratio may be increased up to a very high number.
U.S. patent application Ser. No. 08/920,716 filed Aug. 29, 1997 discloses a wireless communication system which is reconfigurable to accommodate varying traffic density by using a flexible optical interface between a base station controller and several base stations. A flexible optical interface is positioned at one or more of the base stations. Communication is provided over an optical fiber, and optical network units associated with each base station include control means for selecting the appropriate wavelengths from the optical fiber for use by that base station. The wavelength selection is provided in both the upstream and the downstream direction.
One drawback of this arrangement is that it is required to provide wavelength selection means in the optical network unit associated with each base station, which increases complexity, costs, maintenance and space requirements for each base station.
It is therefore an object of the present invention to provide a reconfigurable wireless network that minimizes the complexity of the base stations.
The present invention provides a wireless communication system comprising a base station controller and a base station interface connected to the base station controller by a central optical fiber. The base station interface may include a flexible wavelength router. At least one base station is connected to the base station interface, and the central optical fiber carries at least one communication channel associated with an optical signal having one of a plurality of wavelengths. The base station interface selectively provides a communication path between the base station controller and at least one base station using at least one communication channel.
The central optical fiber may carry a plurality of communication channels each associated with an optical signal having one of a plurality of wavelengths. The base station interface selectively provides a communication path between the base station controller and the base station using at least one of the plurality of communication channels.
A plurality of base stations may be connected to the base station interface. The base station interface selectively provides communication paths between the base station controller and selected ones of the plurality of base stations using the at least one communication channel.
The base station interface may provide communication paths between the base station controller and the plurality of base stations using the plurality of communication channels, where each communication path including one or more communication channels.
The present invention also provides a wireless communication system comprising a base station controller and a wavelength flexible router connected to the base station controller by a central optical fiber. A plurality of base stations are connected to the wavelength flexible router. The central optical fiber carries a plurality of communication channels each associated with an optical signal having one of a plurality of wavelengths. The wavelength flexible router selectively provides a communication path between the base station controller and at least one of the plurality of base stations using at least one communication channel, wherein at least some of the functionality associated with each base station is performed at the base station controller.
The functionality performed at the base station controller may include mobility-related functions, such as macro-diversity handling. The functionality performed at the base station controller may also include generating and receiving the analogue signals to and from the antenna.
The invention thus provides for the centralization of base station functions at the base station controller site, thus giving optically remote antenna sites.